In conventional constant velocity transport (CVT) simplex and duplex scanning systems, users typically must choose between either productivity or individual image size detection, for mixed size documents. An example of such a system is disclosed in U.S. Pat. No. 5,946,527, herein incorporated by reference in its entirety. The choice between these scanning modes is not always transparent to the user.
For example, if a user selects full productivity then the system will use the largest paper size detected, via sensors in the document handler, for all document scanned in the stack. If the sensors detects that the largest paper size is letter sized (i.e., 8½×11 inches), all documents will be scanned to electronic image data generally corresponding to that image size, even though some of the documents may actually be smaller.: This may be an inefficiency use of memory resources for mixed sized documents. For instance, a 5×7 inch document also scanned would not require the same number of pixels as a letter sized document. Thus, many pixels would simply be simply be nil (or perhaps, treated as white).
On the other hand, if the user selects individual image size detection then the system must scan each image twice. The first pass detects the size of all sheets in a first low-resolution scan and the second pass scans each sheet in a second high-resolution scan based on the size information determined during the first scan. Both modes reduce scanning efficiency.
Also, in conventional single pass duplex scanning systems it is necessary to have multiple channels of electronics all the way through the system into main scanner image memory. This burdens the system with the additional costs for multiple paths of electronics and multiple interfaces (such as cables). Further; this makes it difficult to add a duplex feature to a base simplex model without a major change in electronics or burdening the base model with added expenses.